Significant research effort has been put into the formulation of improved design procedures for the calculation of the axial capacity of open-ended piles in sand. Methods, such as the Imperial College Pile (ICP) and the University of Western Australia (UWA-05), estimate the medium-term capacity of piles at relatively large displacements (typically 10% of the pile diameter). To use these approaches in pile driveability analyses, some additional factors need to be taken into account. In addition to the significant influence of dynamic effects, such factors include the absence of pile ageing and the relatively low displacement mobilised during individual hammer blows. In this paper, pile driving records from the installation of two open-ended steel piles installed in medium dense to dense North Sea sand are considered. The piles are a 0.762m-diameter skirt pile supporting a jacket structure and a 4.2m-diameter monopile, respectively. The piling records are used to test the accuracy of existing pile driveability models by comparing the measured and predicted blow counts. The latter are determined by incorporating the static resistance to driving (SRD) and dynamic damping parameters in a 1D wave equation analysis program. The possibilities of using recent static capacity formulae (e.g. ICP and UWA-05) to predict driveability were also explored.
Pile driveability is an integral component of the process of offshore pile design and is often the determining factor in the selection of an appropriate driving system. Accurately predicting the pile response to driving is becoming increasingly important, with the use of large 3–6m diameter steel monopiles becoming commonplace. Pile driveability assesses the ability for a pile to be economically driven with an acceptably low risk of refusal and, ultimately, to reach a desired penetration or capacity within a reasonable number of blows without overstressing the steel.
